This invention is directed to telephone communications systems and, more particularly, circuitry useful in coupling DTMF receivers to pulsing relays, particularly pulsing relays used in orginating registers, such as the "L" relay used in a #5 Crossbar Originating Register.
In many environments where it is necessary to convert dual tone multifrequency (DTMF) signals of the type produced by a pushbutton telephone into rotary dial type pulses, a tone-to-pulse converter (DTMF receiver) provides an output that splits the tip and ring lines during a conversion sequence. During conversion, the DTMF receiver receives and converts DTMF signals into rotary dial type pulses and the pulses are outpulsed beyond the line split. However, in certain environments, this arrangement is unsatisfactory. Specifically, attempts to use this arrangement is certain central office equipment, such as a #5 Crossbar Originating Register, results in the production of annoying line clicks on a subscribers line due to line splitting by the tone-to-pulse converter. Other service related problems can also occur. For example, coin telephone and tip-party interrogation signals from the originating register can be partially or entirely blocked during the line split period of time.
One proposal to overcome the foregoing disadvantage is to avoid splitting the line and pulsing the primary winding of the line relay (commonly referred to as the L-relay) of the originating register. (The line or L-relay is the relay having a primary winding that responds to rotary dial pulses and, in accordance with the receipt of rotary dial pulses, opens and closes relay contacts connected to pulse count (e.g., P) relays, which form a dial pulse counter.) This proposal also has disadvantages. Specifically, pulsing the primary winding of the line relay based on the output of a DTMF receiver results in the production of a system that is incompatible in some instances with some of the test equipment normally associated with such central office equipment, such as the Automatic Monitor Register and the Sender Test Circuit, commonly known as the Master Test Frame.
In order to overcome the test equipment incompatability problem pulsing of the contact terminals (rather than the primary winding) of the L-relay in a manner that simulates the exact way an L-relay responds to rotary dial pulses has been proposed. While this solution overcomes the disadvantages of pulsing the primary winding of the L-relay, it produces other problems. Specifically, pulsing all of the contact terminals of the L-relay, in the same manner as they would be opened and closed by rotary dial pulses pulsing the primary winding of the L-relay, results in the creation of undesirable clicks or pops on the telephone line. Because the clicks or pops are audible to the subscriber, service complaints are likely to occur. Thus, this proposed solution is also unsatisfactory.
Therefore, it is an object of this invention to provide an apparatus for coupling a DTMF receiver to an originating register in a manner such that the functional operation of the originating register, including the functional operation of items such as the Master Test Frame, is not inhibited and in a manner such that undesirable subscriber audible signals are not produced.
It is another object of this invention to provide a tone adaptor pulsing circuit for pulsing the terminals of a line or L-relay in a manner such that undesirable subscriber audible signals are not produced.
It is a still further object of this invention to provide a tone adaptor pulsing circuit suitable for pulsing the terminals of a line or L-relay in a manner that simulates the dial pulse counting action that would occur if the primary winding of the relay were pulsed by dial pulses, without creating undesirable audible effects.